In order to transmit large volume data at limited frequencies, there has been advanced development of multiple input multiple output (MIMO) system in which spatial multiplex transmission is performed using a plurality of transmitting and receiving antennas. In recent years, with the aim of further improving frequency utilization efficiency, use of higher frequencies and multi-element configuration of antenna elements have been promoted, and it is expected that the number of spatially multiplexed objects will continue to increase in the future.
In a radio transmission apparatus, a high power amplifier (HPA) for emitting a signal from an antenna is necessary. A multicarrier scheme such as orthogonal frequency division multiplexing (OFDM) is used as a wireless transmission system suitable for high volume transmission, but this scheme is known to have a large peak to average power ratio (PAPR). In order to accurately transmit a signal with a large PAPR, the HPA is required to have precise linearity, and there is concern that the cost will increase. When combining the multicarrier scheme and the MIMO system, it is necessary to take account of a larger PAPR, so the above-mentioned linearity problem becomes more serious.
As a technique for dealing with a large PAPR, for example, in Non Patent Literature 1, a PAPR is minimized by applying a time filter to an instantaneous value of a waveform with a large time fluctuation thereby to mitigate an influence thereof on an amplifier. In Non Patent Literature 2, a technique is disclosed in which a multi user (MU)-MIMO system is assumed, and with the use of a carrier and noise power ratio (CNR) fed back from a receiving side, a transmitting side adaptively controls backoff based on a predicted carrier and interference noise power ratio (CINR) calculated from backoff of an HPA.